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M. R. Showalter (Stanford)
Closeup Voyager images of Saturn's F Ring have long been known to show a variety of kinks and clumps as well as the so-called ``braids.'' Recent dynamical simulations reveal how gravitational perturbations by Prometheus can explain some and perhaps all of these peculiar features. I have re-projected all of the closeup Voyager images into a common geometry to facilitate comparisons to the models. Adjacent images taken at the same time are merged into mosaics. Simulations consist of a sector of the ring containing ~ 3000 massless, non-interacting test particles, perturbed by Prometheus on its eccentric orbit. For each image, I have simulated the ring under dynamical circumstances that match the actual ring/Prometheus encounter geometry, where the ring sector is initially uniform.
Simulations show that bright clumps are often displaced radially relative the ring itself, in a manner consistent with the appearance of the ring's kinks and clumps. This investigation also provides a natural explanation for the ``braids.'' We know that some F Ring images show multiple strands. In addition, the tracking of ring clumps reveals that they have different mean motions, suggesting that individual strands are likely to be incomplete and/or variable in brightness. The mysterious braid images may be showing nothing more than two non-interacting, incomplete strands in which the radial distortions from Prometheus are 180\circ out of phase. The most apparent difference between images and simulations is that the latter always show a 3.2\circ periodicity expected for perturbations from Prometheus. In the images, these periodicities are often but not always present. This appears to be related to the fact that the ring does not return to uniformity between Prometheus encounters.
This work is supported by NASA's Planetary Geology and Geophysics Program.